• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.4
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• pp.629-635
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• 2017

Free-Flooded Ring (FFR) transducer array for use in Sonar system can be driven with large amplitude in a wide frequency band due to its structural characteristics, in which two resonances of a ring mode (1st radial mode) and an inner cavity vibration mode occur in a low frequency band. Since its sound wave generation characteristics are not influenced by the water pressure, the FFR transducer array is widely used in the deep sea. So FFR has been recognized as a low-frequency active sound source and has received much attention ever since. In order to utilize the FFR transducer array for SONAR systems in military and industrial applications, its equivalent electric circuit model is necessary especially to design the matching circuit between the driving power amplifier and the FFR transducer array. Thus this paper proposes the equivalent electric circuit model of FFR transducer array by using measured values of parameter, and suggest the improved method of parameter identification. Finally it verifies the effectiveness of the proposed circuit model of FFR transducer array by experimental measurements.

• Structural Engineering and Mechanics
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• v.76 no.1
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• pp.141-151
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• 2020

This manuscript tends to investigate influences of nanoscale and surface energy on a static bending and free vibration of piezoelectric perforated nanobeam structural element, for the first time. Nonlocal differential elasticity theory of Eringen is manipulated to depict the long-range atoms interactions, by imposing length scale parameter. Surface energy dominated in nanoscale structure, is included in the proposed model by using Gurtin-Murdoch model. The coupling effect between nonlocal elasticity and surface energy is included in the proposed model. Constitutive and governing equations of nonlocal-surface perforated Euler-Bernoulli nanobeam are derived by Hamilton's principle. The distribution of electric potential for the piezoelectric nanobeam model is assumed to vary as a combination of a cosine and linear variation, which satisfies the Maxwell's equation. The proposed model is solved numerically by using the finite-element method (FEM). The present model is validated by comparing the obtained results with previously published works. The detailed parametric study is presented to examine effects of the number of holes, perforation size, nonlocal parameter, surface energy, boundary conditions, and external electric voltage on the electro-mechanical behaviors of piezoelectric perforated nanobeams. It is found that the effect of surface stresses becomes more significant as the thickness decreases in the range of nanometers. The effect of number of holes becomes significant in the region 0.2 ≤ α ≤ 0.8. The current model can be used in design of perforated nano-electro-mechanical systems (PNEMS).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.2 no.3
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• pp.75-86
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• 1982

The degeneration of two classes of thick beam elements has been conducted, one (DB6) based on the conventional Timoshenko beam assumptions whereas the other (DB7) based on the assumed cubic axial displacement profile. While an adjustable shear correction factor is required for the DB 6 element to compensate for the unrealistic distribution of shear strain across the thickness, the DB 7 element assumes the more realistic quadratic profile of shear strain at the outset. With the plane-stress continuum solution as reference, solutions obtained by these two element models are compared with the analytical Timoshenko solution, the analytical thin beam solution and several available solutions of other existing beam elements. The result indicates that the performance of the higher order beam element DB 7 is consistently superior to any others. This is true for the whole range of aspect ratios of beam, in both static and free vibration analyses.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.4
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• pp.329-335
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• 2014

This study aimed to understand the internal flow characteristics of a liquid droplet subject to periodic forced vibration. In order to predict the resonance frequency of a droplet, a high-speed camera and macro lens were used to capture internal flow characteristics of a droplet placed on a vibrating hydrophobic surface. Results showed that the droplet assumed a variety of shapes depending on the resonance mode of free droplet, particularly in modes 2, 4, 6, and 8. In addition, the induced internal vortex flow inside the droplet was also observed in each mode. Typically, the induced flow moved upwards along the axis of symmetry and downwards along the surface of the droplet, that is, from the apex to the contact line in modes 2 and 4, after which it broke into a smaller vortex. On the other hand, the large-scale vortex always remained steady in modes 6 and 8. The speed of the flow in mode 4 was always greater than that in mode 2, but those in modes 6 and 8 were similar.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.2
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• pp.99-105
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• 2017

Wind tunnel test which is one of the method to predict the aeroelastic characteristics has difficulties to make scale-down structural model and achieve a specified free stream velocity. It is very costly and complicated to consider similarity relationships between real structure and scale-down structural model. "Dry Wind-Tunnel(DWT)" was proposed to overcome these difficulties. This is made up of Ground Vibration Test hardware and software to compute the aerodynamic forces. In the present study, program for computing the real-time unsteady aerodynamic forces which is an important part of DWT system was developed by Matlab Simulink and dSPACE. In addition, using this program and software which is a part of the test structure, a real-time flutter analysis was conducted and the results are verified by ZAERO.

• Journal of Korean Society of Steel Construction
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• v.13 no.6
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• pp.703-713
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• 2001

Derivation procedures of exact dynamic stiffness matrices of thin-walled straight beams subjected to eccentrically axial forces are rigorously presented for the spatial free vibration analysis. An exact dynamic stiffness matrix is established from governing equations for a uniform beam element with nonsymmetric thin-walled cross section. First this numerical technique is accomplished via a generalized linear eigenvalue problem by introducing 14 displacement parameters and a system of linear algebraic equations with complex matrices. Thus, the displacement functions of displacement parameters are exactly derived and finally exact stiffness matrices are determined using element force-displacement relationships. The natural frequencies of nonsymmetric thin-walled straight beams are evaluated and compared with analytical solutions or results by thin-walled beam element using the cubic Hermitian polynomials and ABAQU's shell elements in order to demonstrate the validity of this study.

• Journal of Korean Society of Steel Construction
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• v.20 no.6
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• pp.761-771
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• 2008

When the crossing frequency of a train meets the natural frequency of a railway bridge, the bridge is bound to become resonant. There are few available time response samples involving a train that passes a bridge at high speed. Very effective modal-parameter extraction techniques for such special high-speed railway bridge conditions are introduced in this paper. Utilizing the cross-correlations of the free-vibration responses after the train passes, mode shapes and the temporal modal parameters (e.g., natural frequency and damping ratio) are extracted using the TDD and SI techniques, respectively. This approach has been applied to a two-span steel composite bridge in the Kyung-Bu high-speed railway system. The estimation results were compared with those obtained using the existing methods. The results fully coincide with those that were extracted using the existing aforementioned technique.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.77-77
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• 2009

ELV(; End of Life Vehicles)를 비롯한 최근 환경 동향은 자동차 전장 모듈에 대하여 다양한 무연 솔더 적용을 요구하고 있다. 특히 자동차 엔진룸과 트랜스미션은 가동 중 고온 및 진동의 지속적인 영향을 받기 때문에 이와 유사한 환경에서의 신뢰성 연구가 필요한 시점이다. 이에 본 연구에서는 Sn3.5Ag, Sn0.7Cu, Sn5.0Sb 솔더 조성에 대하여 복합환경 조건하에서 접합부 신뢰성을 평가하였다. 복합환경을 구현하기 위하여 $-40{\sim}150^{\circ}C$ 범위의 온도 사이클과 랜덤 진동을 동시에 인가하였으며, 진동 가속도 3G, 진동주파수는 10~1000Hz 로 설정하여 자동차 환경을 충족하였다. 복합시험의 1 cycle 은 20 시간이며, 총 120 시간의 시험 동안 진동의 영향 및 진동과 고온이 동시에 작용하였을 경우의 영향에 대해 비교하였다. 테스트 모듈 제작을 위해 450 um 의 솔더볼이 적용되었으며, 각 조성의 솔더볼을 이용하여 BGA test chip 제작하였고, 제작된 BGA test chip 은 다시 daisy chain PCB 위에 실장 및 리플로우 공정을 통해 접합되었다. 테스트 동안 In-situ 로 저항의 변화를 관찰하여 파단의 유무를 판단하였고 전자주사현미경을 통해 파괴 기전을 평가하였다. 복합시험 시간에 따른 전단강도를 측정하였으며, 각 조성에 대하여 상이한 전단강도 변화를 관찰하였다. 계면 IMC 형상은 전단강도 변화에 영향을 주었으며, 특히 높은 온도가 IMC 성장을 촉진시켜 전단강도 감소에 영향을 주었다. 본 복합환경 시험 조건에서는 Sn0.7Cu 가 가장 안정적이었으며, 파단면을 관찰한 결과 연성파괴 모드가 관찰되었다.

• Journal of the Korean Wood Science and Technology
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• v.42 no.6
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• pp.723-731
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• 2014

Nondestructive evaluation (NDE) technique method using a resonance frequency mode was carried out for ceramics made by different carbonizing temperatures (600, 800, 1000, $1200^{\circ}C$) after impregnating the phenol resin with Miscanthus sinensis var. purpurascen particle boards. Dynamic modulus of elasticity increased with increasing carbonizing temperature. There were a close relationship of dynamic modulus of elasticity and static bending modulus of elasticity to modulus of rupture (MOR). However, the result indicated that correlation coefficient was higher in dynamic modulus of elasticity to MOR than that in static modulus of elasticity to MOR. Therefore, the dynamic modulus of elasticity using resonance frequency by free vibration mode is more useful as a nondestructive evaluation method for predicting the MOR of ceramics made by different carbonizing temperature for Miscanthus sinensis var. purpurascens particle boards.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.48-55
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• 2018

The purpose of the present study is to compare the reduction rate of natural frequency and the increase rate of damping parameter with structural damage in system. For this purpose, experiment and numerical simulation analysis are performed for the 2-span H-Beam with lower natural frequency and higher damping parameter from free vibration in structure. The response signal by impact load before and after damage is analyzed at 14 locations. The response signals for all locations are performed fast fourier transform to estimate the natural frequency reduction rate and wavelet transform to estimate the damping parameter increase rate. The time domain function corresponding to each scale(frequency) is separated from the response signal by wavelet parameter. The estimation of damping parameter increase rate using wavelet transform is more sensitive than the estimation of natural frequency reduction rate in structure.